Squashfs: update Kconfig and documentation for LZO

Update compression types supported and add some help text for
the LZO Kconfig option.

Also add missing "default n" line and make some trivial whitespace
cleanups too.

Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>

Documentation/filesystems/squashfs.txt

@@ -2,7 +2,7 @@ SQUASHFS 4.0 FILESYSTEM
 =======================
 
 Squashfs is a compressed read-only filesystem for Linux.
-It uses zlib compression to compress files, inodes and directories.
+It uses zlib/lzo compression to compress files, inodes and directories.
 Inodes in the system are very small and all blocks are packed to minimise
 data overhead. Block sizes greater than 4K are supported up to a maximum
 of 1Mbytes (default block size 128K).